Lung cancer is the leading cause of cancer death in the U.S., but the good news is that the rate of new cases is decreasing — largely due to people either stopping smoking or never starting in the first place.

In addition, thanks to lung cancer screening, there's even more that can be done to reduce lung cancer deaths.

"We've always known that the earlier we catch lung cancer the better," says Dr. Houssam Oueini, a pulmonologist at Houston Methodist. "There is a huge survivability gap between when we catch it early versus late."

For instance, the 5-year survivability of stage 1 lung cancer is about 85%. This rate drops to just 20% if lung cancer isn't caught until stage 4.

"So the question is: What's the best way to catch it?" adds Dr. Oueini. "That's where lung cancer screening becomes important."

What is lung cancer screening?

It's worth discussing how lung cancer screening has evolved over time.

"In the 1990s, we used chest X-rays and sputum samples," explains Dr. Oueini. "Neither approach was very successful in showing benefit for catching lung cancer early."

In the early 2000s, CT (computed tomography) scans became the predominant method of screening for lung cancer. Unlike a flat, 2D chest X-ray, a chest CT scan involves taking several X-ray images and processing the images to create a more detailed, cross-sectional view of the lungs.

Lung cancer screening requires only a low-dose CT scan, meaning less radiation is needed than during a regular CT scan, and it can be performed without contrast dye, so an IV isn't needed. The screening is covered by insurance for those who meet eligibility criteria.

"The person simply lies on the table and goes through the tube for 30 seconds," explains Dr. Oueini. "Then they're done."

And low-dose CT scans of the lungs work. A large study demonstrated that this method of screening improved the length of life of people diagnosed with lung cancer. But early lung cancer CT screening was restricted only to those at very high risk for lung cancer. Screening guidelines subsequently were relaxed — the age criteria was widened — but remain restricted to those at high risk.

"If something looks abnormal on a CT scan, the next step is to take a biopsy," says Dr. Oueini. "At that time, the only way to perform a lung biopsy was through a surgical procedure."

Surgical lung biopsy isn't trivial. There's a risk of complications, so doctors only perform the procedure when it's really needed.

Fortunately, biopsy technology has improved, making today's procedure much safer.

"The advancement of robotic bronchoscopy now means a person doesn't have to go through surgery for us to biopsy the lung," says Dr. Oueini. "And safer biopsying meant the guidelines of who should be screened for lung cancer could be relaxed."

Lung cancer screening guidelines: Who's eligible?

Smoking cigarettes is the No. 1 risk factor for lung cancer, and screening eligibility hinges on this.

"Right now, we only screen people who are current or former heavy smokers — defined as having a 20-pack-year smoking history," says Dr. Oueini. "Age and how long it's been since quitting come into play, as well."

These criteria may relax even further soon. Just last week, the American Cancer Society recommended that all former smokers with a 20-pack-year history should be eligible for screening, regardless of how long ago they quit. The organization calculates that such eligibility expansion will help avert 21% more lung cancer deaths. It may be several months before these recommendations are considered and implemented.

Importantly, lung cancer screening isn't just a one-time thing.

"You have to do it every year until you are outside of either the age range or it's been more than 15 years since you quit smoking," says Dr. Oueini. "This annual nature is one reason why adherence to lung cancer screening is limited, but it's incredibly important that eligible individuals stay committed."

Why you shouldn't delay or ignore lung cancer screening

Though a very efficient tool, adherence to lung cancer screening is a challenge.

"Abidance by the current guidelines is less than 10%," says Dr. Oueini. "This means that for every 10 people eligible, only one is actually coming in to get screened, on average."

Whether it's anxiety about the possibility of a positive result or guilt about your current or past smoking history, don't let anything keep you from coming in for screening if you're eligible.

For starters, getting a call back doesn't automatically mean you have lung cancer.

"The majority of positive findings are actually noncancerous," adds Dr. Oueini. "But we need to evaluate every finding until cancer can confidently be ruled out."

Dr. Oueini likens this to finding a mole on the skin. The majority of us have at least one mole, but not every mole is cancer. Still, they should be evaluated by a specialist to ensure they're not cancerous.

"We want to catch lung cancer as early as possible," says Dr. Oueini. "It's understandable to be anxious about potentially uncovering something, but the reality is that, even if it is lung cancer, the outcomes are so much better if it's caught before it progresses and spreads."

Don't ignore lung cancer symptoms, even if you're not eligible for lung cancer screening

Screening helps catch more lung cancers, but this doesn't mean that people who don't fit the criteria can't develop lung cancer.

"We know that lung cancer isn't only caused by smoking," says Dr. Oueini. "Environmental factors — exposure to asbestos, smoke from fires and industrial pollution — are also risk factors."

Due to lack of data, these factors aren't considered in the current screening guidelines, but Dr. Oueini believes there may come a day when, like mammograms, lung cancer screening is dictated solely by age.

In the meantime, it's why everyone should take lung cancer symptoms seriously, which include:

• Chronic cough
• Coughing up blood
• Unintentional weight loss
• Chest pain that can't be explained by other findings

"If you have symptoms of lung cancer, you need to be evaluated," says Dr. Oueini. "Don't delay."